为什么这个 [Swift] NSObject.addObserver 注册没有按预期调用 func observeValueForKeyPath()？

Question

下面是有问题的代码。 [我希望]问题在上面的问题中得到了完整的概述。提前致谢。 MJB.

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate
{
    var some_string:NSString = "one"

    func application ( application: UIApplication, didFinishLaunchingWithOptions launchOptions: [NSObject: AnyObject]? ) -> Bool
    {
        println("init...")
        self.addObserver( self, forKeyPath: "some_string", options: nil, context: nil )
        self.some_string = "two"
        return true
    }

    override func observeValueForKeyPath ( keyPath: String, ofObject object: AnyObject, change: [NSObject : AnyObject], context: UnsafeMutablePointer<Void> )
    {
        println("observeValueForKeyPath...")
    }
}

Answer 1

根据 Apple Documentation，您需要使用 dynamic 关键字为属性启用 KVO:

dynamic var some_string : NSString = "one"

此外，class 必须继承自 NSObject 才能使这项工作正常进行，但在您的情况下，UIResponder.

是给定的

为什么这个 [Swift] NSObject.addObserver 注册没有按预期调用 func observeValueForKeyPath()？

Why might this [Swift] NSObject.addObserver registration not be calling func observeValueForKeyPath() as expected?

swift

xcode6

addobserver